SEED-BEARING PLANTS 477 
tion of flower-structure (Fig. 359). The deeply five-parted 
and reflexed corolla bears a crown of five "hooded" bodies, 
in each of which there arises a pointed, incurved "horn" 
(Fig. 360). The anthers are more or less united around the 
stigma, and each cell contains a waxy, pear-shaped pollen- 
mass (pollinium) . The pollinia of adjacent anthers adhere 
in pairs to cleft glands that grow one on each of the five 
angles of the stigma. As bees climb over the flowers in 
search of nectar in the bottom of the hoods, their legs 
are drawn through tiny slits, and catch the cleft gland 
FIG. 361. Milkweed (Asclepias) . Pollen-mass (pollinium), showing 
germination. 
when pulled out. Often the gland cannot be loosened, 
and the legs of the insects are pulled off and left attached 
to the flower. When the insect visits another flower the 
pollen-masses (which by this time have twisted and 
folded together) become inserted into the stigmatic 
chamber of the second flower, where they germinate, 
sending out numerous pollen-tubes (Fig. 361). On ac- 
count of the complicated nature of this process, pollina- 
tion often fails, so that only a small percentage of the very 
numerous flowers produces seed. After fertilization, the 
carpels increase enormously in size, and ripen into a pod, 
filled with a large quantity of flat, thin seeds, each of 
